The toothed timing belt that is spanned over toothed pulleys on the drive and cam shafts of a motor-vehicle internal-combustion engine must be tensioned by a third element, since the radial spacing between the drive and camshaft pulleys is invariable. The belt cannot even be mounted in place unless it is long enough to fit over these two fixedly spaced pulleys. Hence a tensioner is used which is normally mounted on a bar formed at one end with a circular throughgoing hole and at its opposite end with an arcuate slot having a center of curvature at the hole of the other end. A wheel carried on a bearing is provided midway between these ends. A bolt passing through the circular hole acts as a pivot and a bolt passing through the arcuate slot in the other end can be tightened to lock the tensioner in any of a plurality of angularly offset positions. The wheel is pressed against the untoothed outer side of the timing belt until the proper tension is obtained, and then the bolt in the slot is tightened to secure the tensioner in place with the set degree of tension.
The timing belt moves at relatively high speed, so a high-quality roller bearing must be provided between the wheel and the axle carrying it. Such a high-quality bearing must have hardened races for the roller elements.
It has been suggested in German patent document No. 2,839,721 filed Sept. 13, 1978 by R. Polster and F. Willert to use a so-called integral inner race which functions as the inner race and axle of the bearing. This inner race is therefore constituted as a short steel pin whose one end is surface hardened to act as a race for the roller elements, and whose other end is unhardened so that it can be mounted by being spread, rivet-fashion, in a hole formed in the support bar of the tensioner.
Producing such an integral inner race, with one hardened end and an opposite unhardened end, is relatively expensive. The advantages of being able to cheaply mount the integral inner race on the support bar by spreading it like a rivet are therefore largely lost to the increased production costs entailed in hardening the outer end.
It has been suggested in German patent document No. 2,224,111 to extend the hardened inner race of a bearing and form it with an outwardly directed ridge over which a dust cap can be snap fitted. Such a structure has not been found to be adaptable to use in a timing-belt tensioner however, as it does not provide a connection rugged enough to allow the bearing itself to be mounted by means of this ridge with sufficient strength to withstand the considerable radial canting forces encountered by a belt tightener.